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Thread: vapor barrier

  1. #16
    Join Date
    Jan 2007
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    Brooklyn, Fire Island
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    Default Re: vapor barrier

    And if you don't want to have to wait for the books, you can download PDF's from here:

    http://www.ecodes.biz/list_sub.cfm?m_cat_id=22
    Francois


    Truth is just one man's explanation for what he thinks he understands. (Walter Mosley)

  2. #17
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    May 2005
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    Default Re: vapor barrier

    I grew up just east of your location and I know the winters are very cold and the summers are very hot and humid. In the winter moisture is likely to move outward and in the summer it is likely to move inward especially for masonry veneer walls. It would not be wise to try to control moisture movement in a wall in your area using only the prescriptive requirements of any model national building code and the code authors don't expect you to.

    The 2003 IRC (I will assume this is a detached residence) allows 3 exceptions for the vapor retarder requirement. The walls of your project do not appear to qualify for Exceptions numbers 2 and 3 (vented cavity and table N1101.2 footnote a).

    Exception number 1 allows the vapor retarder to be omitted "in construction where moisture or freezing will not damage the materials". This means, for example, if there is sufficient rigid closed-cell foam insulation on the exterior of the building envelope (frame) that the condensation (dew) point in winter will fall within the foam insulation, an interior vapor retarder is not required (although one might be placed elsewhere). This wall would be able to dry to the inside in summer making it appropriate for climates with wide climate extremes like central Missouri. This is, of course, a simple example; there are many variations on this concept and they are accepted by building officials all over the US under the IRC.

    That's all I can tell you without knowing more about the project. But it is, without question, your architect's responsibility, not the building code, to determine the construction of the wall system with the help of a qualified HVAC designer if he needs one.
    Last edited by Sweep8; 10-11-2007 at 10:35 AM.

  3. #18

    Default Re: vapor barrier

    Let me explain this in more detail.

    This is not a residence--it is a religious building. I am trying to prevent mold problems in this building. This architect has used this identical wall system on hundreds of buildings--many of them have mold problems. However, what is the cause of the mold problems? Not his design, of course not!

    This building is, from outside in: masonry; vented cavity; housewrap; OSB; fiberglass insulation and wood framing; 6mil poly; drywall; paint. I subscribe to the philoslphy that you DO NOT want the 6mil poly because it will not allow proper dry-through. He claims that you must have the poly to protect the inside of the wall from all of the moisture expelled by occupants when they exhale. But, he also claims that the code REQUIRES it.

    I want to prove to him that the code does not REQUIRE it. I want him to try it my way just once and see if a mold problem occurs. Basically, I subscribe to what www.buildingscience.com says.

  4. #19
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    Default Re: vapor barrier

    That wall section would be OK in winter. And OK immediately after construction IF kiln- or air- dried wood was used, and things did not get wet during construction. The assembly can dry to the exterior, via the gap between brick and WRB.

    The challenge is to BE SURE that the space is, in fact there, and not clogged with mortar droppings.

    The wall section will be a PROBLEM in the summer, assuming the building is air conditioned. On hot, humid days the moisture will want to condense on the cool, outside surface of the poly. That puts the condensed, bulk water INSIDE the wall assembly. From whence all hell breaks loose.

    Go for a code-approved compromise. Delete the poly. Instead used kraft faced batt insulation. If he really insists on a sheet good, then change from poly to Membrain.

  5. #20
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    Jun 2004
    Location
    Northwest lower MI
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    Default Re: vapor barrier

    And don't waste your money buying the IRC. It only applies to detached 1 & 2 Family Dwellings and Townhouses 3 stories or less above grade.

  6. #21
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    Default Re: vapor barrier

    Roger, Roger.

    I was also just doing some filing and EEBA guide to Mixed-Humid climates passed through my hands. Without rereading all the posts, I recall you are in MO??? If so, thats your climate, and, vapor retarders are installed on the EXTERIOR sides of walls of air conditioned buildings where you are.

    Frankly, you are in the zone we used to define as "when in doubt, leave it out".

  7. #22
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    Northwest lower MI
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    Default Re: vapor barrier

    NW :
    You're confused. I'm in NW Lower Michigan. jeffrsapp is building in MO.

  8. #23
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    Default Re: vapor barrier

    Bad english on my part.

    "Roger, Roger" was meant for you

    The rest was meant for the poster in MO (which I now see is not the location of the original poster) This thread appears to have started in Indiana, and would up in Missouri. NEWBIES: read thread with care. Its got info applicable to two different situations!

  9. #24

    Default Re: vapor barrier

    Sorry for the confusion! I didn't want to start a new post because this post seemed to be applicable.

    YES, I AGREEE--LEAVE IT OUT! I have tried over and over and over and over to explain this to this architect, but he just can't seem to get it through is head. WE AREN'T IN ALASKA ANYMORE! WE ARE IN MISSOURI!

    I appreciate everybody's input on this matter. But, I did want to make something clear: Are you telling me that the IBC will say in writing somewhere that in Missouri, a vapor barrier is NOT required? If so, please tell me exactly where it states that. I have the book, but I have not found it!

  10. #25
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    Default Re: vapor barrier

    Should be 1403.3, but I can't tell you what the original IBC says there - my copy has an Oregon amendment at that location

  11. #26
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    crested butte colorado
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    Default Re: vapor barrier

    Jeff, I did some WUFI tests on a wall similar to what you describe, and for a st louis climate. If the church is only filled on sunday you can safely skip the retarder, but if it is full. ie humid because of all the people breathing on a regular basis then even the class 1 vapor barrier will be a good thing. If I run the wall as a high humidity home with AC then the OSB shows some big moisture spikes when only latex is used as the retarder. I bet you can get the architect to meet you in the middle, and use either a smart vapor retarder, kraft covered batts, or a vapor retarder paint on the inside. all of these options would meet what the guy thinks the code states.

  12. #27
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    Default Re: vapor barrier

    Ok, so now we know it's a church with brick veneer; that's different.

    The 2003 IBC (1403.3) requires a vapor retarder but it doesn't say where to put it (or in what region it is not required) because it is not a prescriptive code (like the IRC); it assumes professional design. This interpretation is supported by the listed Exception that the retarder is not required "Where approved means to avoid condensation and leakage of moisture are provided." "approved" is defined by the IBC as "acceptable to the building official". "approved source" is defined as "an independent person, firm or corporation, approved by the building official, who is competent and experienced in the application of engineering principles to materials, methods or systems analyses", in other words a professional designer. So, the architect is expected to design the wall system and the IBC is not going to tell you how to do that.

    www.buildingscience.com recommends that mixed-humid climates be designed as follows:

    "For mixed-humid climates, walls are generally designed to dry to both the interior and the exterior (flow through assemblies) or, they are designed with insulating sheathing in order to control the temperature of the condensing surfaces. The thickness of the insulating sheathing is determined by calculation based on the severity of the climate."

    " ... 1 inch of rigid insulating sheathing is designed to elevate the condensing surface in the wall assembly to reduce the risk of condensation occurring within the assembly. During the winter months, the interior humidity levels should be kept lower to limit the amount of moisture able to diffuse into the wall assembly. During the summer months the vapor drive will primarily be from the exterior to the interior. To accommodate this, the assembly is designed to be able to dry to the interior through the use of semi-permeable latex paint on the interior gypsum. Drying to the interior is important, therefore, interior vapor barriers should not be installed."
    http://www.tiny.cc/vQQoN

    So, put some foam insulation in a 1 3/4" brick cavity and omit the vapor retarder or let the architect keep the vapor barrier and insist on OSB sheathing and Typar housewrap. Then pray it doesn't rain or if it does, turn off the air conditioning and open the windows. Of course, you could just get out while you can.

    By the way, the only reason for a vapor retarder is to prevent moisture that naturally travels through a wall, from a relatively humid space to a drier space, from condensing when insulation has made one side of the cavity considerably colder than the other in any climate. Because this works in both directions, there can be no single prescriptive code solution for a vapor retarder for a location like central Missouri. Any local HVAC designer will be well aware of this and your architect should also. Wherever you place a vapor retarder, it is likely to cause a problem in one season or the other. Omitting the retarder is clearly allowed by the IBC if it is designed properly and that is the architect's job; this is strictly a design issue, not a code issue.

  13. #28
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    Default Re: vapor barrier

    This information is not hard to find in the IBC book. You can look in the index under "vapor retarders" or on the second page of Chapter 14 (Exterior Walls).

  14. #29
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    Default Re: vapor barrier

    This appears to be a moving target.

    IBC 2000
    1403.3 Vapor retarder. An approved interior non-corrodible vapor retarder shall be provided. Vapor retarders shall be tested in accordance with ASTM E 96.
    Exceptions:
    1. Where other approved means to avoid condensation and leakage of moisture are provided.
    2. Plain and reinforced concrete or masonry exterior walls designed and constructed in accordance with Chapter 19 or 21, respectively.


    IBC 2003
    1403.3 Vapor retarder. An approved vapor retarder shall be provided.
    Exceptions:
    1. Where other approved means to avoid condensation and leakage of moisture are provided.
    2. Plain and reinforced concrete or masonry exterior walls designed and constructed in accordance with Chapter 19 or 21, respectively.

    IBC 2006 Deleted. (FS 172-04/05)
    Reason:
    The current Section 1403.3 is inconsistent with Section
    1403.2, which states “Protection against condensation in the exterior wall assembly shall be provided in accordance with the International Energy Conservation Code.” in that the IECC provides an exception to the vapor retarder requirement for several climate zones. The section could be revised to agree with the requirements in the IECC, but as revision to the IECC is underway, the least confusing path is to delete the section from the IBC and rely on the IECC reference.

    Committee Action: Approved as Submitted
    Committee Reason: The section should be removed from the building code, given that the subject is more of an energy code related issue.

    2006 IECC 502.5 (commercial) Moisture control. (Mandatory). ... shall be provided with an approved vapor retarder ...
    Exceptions:
    1. Buildings located in Climate Zones 1 through 3 as indicated in Figure 301.1 and Table 301.1. (MO is Zone 4 and 5)
    2. In construction where moisture or its freezing will not damage the materials.
    3. Where other approved means to avoid condensation in unventilated framed wall, floor, roof and ceiling cavities are provided.

    2007 IECC Suppliment. Section 502.5 Change to read as shown: (EC28-06/07 Part I)
    502.5 Vapor retarders. Class I or II vapor retarders are required on the interior side of frame walls in Zones 5, 6, 7, 8 and Marine 4.
    Exceptions:
    1. Basement walls.
    2. Below grade portion of any wall.
    3. Construction where moisture or its freezing will not damage the materials.

    Additional subsections (including class III VR) also added. See http://www.iccsafe.org/cs/codes/2007...nt/IECC07S.pdf

  15. #30
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    May 2005
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    597

    Default Re: vapor barrier

    Thanks for that research; it's good to have. This issue is a moving target because it is impossible to formulate rules for where a vapor retarder should be placed in all walls; there are simply too many variables involved.

    Why anyone would look to a building code for guidance in the design of a commercial building wall system is beyond me. It's not a manual for good construction; it's a set of minimum standards to help protect the safety of the public. Asking it to design a wall system for you is an invitation to disaster.

    I've been designing buildings for 40 years and the code has rarely had anything to tell me that wasn't related to building limits, fire protection and egress. If you can't figure out where a vapor retarder should go and be able to convince a building inspector that it is acceptable, you should be in a different line of work.

    Sorry, but this issue is starting to annoy me. Next we'll be discussing incompetent architects and I don't need any more of that.

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